Fix up workarounds for dietlibc breakage

Fix up workarounds for dietlibc breakage

The dietlibc doesn't support the TZ environment variable, which is
required by the standard.  Work around this so that we can run the
regression test suite when building with dietlibc.  (This is useful
for finding problems.)

With this change, the only thing which doesn't work as far as dietlibc
is concerned is the posix_memalign test, and the MMP support tests
(because posix_memalign isn't provided by dietlibc, sigh.)

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>